The present invention relates to a method and a device for controlling an exhaust gas aftertreatment system of an internal combustion engine.
A method and a device for controlling an exhaust gas aftertreatment system of an internal combustion engine are described in, for example, German Patent Application No. 199 06 287, in which an exhaust gas aftertreatment system includes a particle filter used, for example, in direct injection internal combustion engines.
Particle filters may become loaded with particles, and regeneration may be performed when a critical amount of particles is exceeded. In this regard, it may be problematic to detect the start and end of the regeneration, as well as to judge whether the particles have been completely regenerated, i.e., oxidized. The differential pressure across the filter may be detected as an output quantity for determining the loading. During regeneration, the resistance of the filter against the medium flowing through decreases, until the value for the empty filter is again achieved, after the reaction of the particles is complete.
The accumulation of ash in the filter may result in a continuous rise in the differential pressure over the operating life of the filter, even in a completely regenerated filter. The additional ash, which may be deposited, may be estimated via fuel consumption and correspondingly considered. Oil ash, which may result from oil consumption in the engine, may not be readily detected. Consequently, increased flow resistance, and thus a rise in the differential pressure, may occur in the completely regenerated filter. As a result, the subsequent regeneration may be initiated too early and/or too often.
By evaluating a first quantity characterizing the oxygen concentration in the exhaust gas upstream from the exhaust gas aftertreatment system and a second quantity characterizing the oxygen concentration in the exhaust gas downstream from the exhaust gas aftertreatment system, and by controlling the regeneration as a function of these quantities, the regeneration may be more precisely controlled.
Two sensors may detect the oxygen concentration, one upstream and the other downstream from the particle filter. The oxygen concentration during regeneration may be lower downstream than upstream from the particle filter, due to oxidation during regeneration.
When regeneration ends, both quantities assume approximately the same value, presupposing that no additional particles are reacted, i.e., oxidized, and that the only particles yet to be reacted are those which have just been emitted from the internal combustion engine. By evaluating both of these signals, the regeneration may be easily and accurately detected. The values may be approximately equal when the difference between the two values corresponds to standard measurement accuracy.
It is believed to be advantageous if the exhaust gas temperature is checked to determine whether it exceeds a specific threshold value, since, only in this case, may oxidation occur, identical oxygen concentrations upstream and downstream from the filter indicating that oxidation has ended.
It is also believed to be advantageous if a differential pressure signal indicating an empty filter is adapted for the detected end of the regeneration. This may permit a significantly more precise control of the start of regeneration.